The silicon based MEMS microphones, also known as acoustic transducers, are playing a more and more important role in the hearing instrument, mobile communication system, digital camera, video camera and toy industry. One of the major issues is to miniaturize the MEMS microphone while still maintaining performances such as sensitivity, noise, compactness, robustness electromagnetic interference (EMI) shielding very well. There have been several attempts made in this respect.
U.S. Pat. No. 6,324,907 discloses a flexible substrate transducer assembly comprising a flexible elongate member, a transducer system, and a lid, wherein the transducer system mounted on the flexible elongate member and covered by the lid includes at least two dies for sensing physical signals and processing electrical signals respectively. The lid and the flexible printed circuit substrate provide good EMI shielding, however, the footprint size of the transducer assembly is large due to an elongate substrate, and the separation of the sensing element and the conditioning integrated circuits requires large package housing.
U.S. Pat. No. 6,781,231 discloses a MEMS package comprising a MEMS microphone including a MEMS acoustic sensing element and conditioning integrated circuits, a substrate for supporting the MEMS microphone and a conductive lid for covering the MEMS microphone. The conductive lid and the substrate can form a housing to accommodate the MEMS microphone and shield the same from electromagnetic interference, however, there are two limiting factors hindering the size reduction of the package herein, i.e. (1) the MEMS acoustic sensing element is separated from the conditioning integrated circuits, and (2) wiring between the integrated circuit element and the substrate takes spaces.
European patent EP 1214864 discloses a sensor system comprising a carrier member, a transducer element, and an electronic device, wherein the transducer element and the electronic device are both bonded onto the carrier member and are electrically interconnected via contact elements held on the carrier member. However, there is no good shielding for the sensor system, and there is no stress buffering between the silicon device and the application printed circuit board (PCB) board.
Therefore, there is a need for a MEMS microphone with a minimized size as well as a good performance, and a method for packaging the MEMS microphone.